Thank you for the hints @ppoirier. Actually, I have read and re-read wiki, warning posts and description of the related parameters multiple times over the past few months and am right now brooding over those very parameters again, just before a maiden flight hopefully later this week…
I find the EK2 sensor fusioning a fairly complex subject, where a number of things are interacting in ways not always readily apparent to me (yet).
Since you seem more knowledgeable in this, may I briefly outline the use situation, and hopefully you could quickly guide in order to reach a solid setup - without 7m/s descents:
- Copter flying outside
- fitted with ToF (Terabee) rangefinder and
- RTK GPS.
- Waypoint/ automatic operation at very low level (3 - 0.3m AGL).
- (some (few) stretches at higher altitude, i.e. when flying to area of operation, or on RTL (ca. 10-15m)).
- Precision altitude control is needed to achieve accurate distance to (mostly only slightly) varying ground levels. This accuracy is only needed on the low descents, at each waypoint, higher portions of the flight do not have to be as accurate.
- WPNAV speeds set very conservative (at first at least)
- NO terrain data stored/ available
- FW currently v. 3.5.7 - necessary/ recommended to upgrade?
Params seeming relevant are set as follows:
AHRS_EKF_TYPE = 2
EK2_ENABLE = 1
EK3_ENABLE = 0
EK2_IMU_MASK = 3 (IMU 1+2)
EK2_GPS_TYPE = 0 (3D velocity & 2D position)
FS_EKF_ACTION = 1 (Land)
EK2_RNG_USE_HGT = 70 (max)
EK2_RNG_USE_SPD = 2
EK2_ALT_M_NSE = 3
TERRAIN_FOLLOW = 0
TERRAIN_ENABLE = 0
RNGFND_MAX_CM = 500
(specs say can do 1400, reports say 500-700 has been tested in sunlight)
I hope the above is correct and suitable for my use case.
I am quite unclear with the following items:
- WPNAV_RFND_USE = 1
- EK2_POSNE_M_NSE = 0.1
- EK2_ALT_SOURCE = 0 or 1??
(0:Use Baro 1:Use Range Finder 2:Use GPS 3:Use Range Beacon)
In conjunction with EK2_ALT_SOURCE the error reports in https://github.com/ArduPilot/ardupilot/issues/7119#issuecomment-396112753 make me unsure: “If someone wants to use range finder all the time, then EKF_ALT_SOURCE = RangeFinder should be used, but not in combination with EKF2_RNG_US_HGT”
How do all those settings look like in your view - correct?
Your comments/ guidance toward changes, particularly to the last two items would be much appreciated to achieve safe, accurate and uneventful flights. Thank you!